The present invention relates to a suspension system adapted to be arranged between members on the body side and wheel side of an automobile, and more specifically, to an improvement of a suspension system having an oil chamber and a gas chamber therein.
A prior art suspension system of an oil-gas pressure type comprises a cylinder housing with a rod fitted therein. A gas chamber and an oil chamber are defined inside the cylinder housing. A high-pressure gas, such as nitrogen, is sealed in the gas chamber. Utilizing the repulsive force of the gas, the system serves as a gas spring. Damping force-generating means is provided inside the cylinder housing. As the oil in the oil chamber passes through the generating means, a damping force is produced by the viscous resistance of the oil, and is used to damp reciprocation of the rod.
Conventionally, a free piston is disposed between oil and gas, in order to prevent the gas in the gas chamber from being absorbed into the oil in the oil chamber. In a suspension system disclosed in U.S. Pat. No. 4,159,756, for example, a seal is provided on the outer peripheral surface of a free piston.
In suspension systems using a free piston, however, considerable frictional resistance occurs at the seal portion, as the piston moves. Moreover, the gas is liable to leak out through the seal portion of the piston, so that it is thus difficult to completely prevent the gas from being absorbed into the oil.
An arrangement has been proposed such that the gas and oil chambers are divided by means of a plastic partition member. However, the plastic member cannot satisfactorily prevent gas permeation. Therefore, prolonged use of the suspension system may possibly cause a gas leak, thereby reducing the capacity of the gas chamber. If the gas chamber capacity lessens in this manner, the spring constant of the system increases. As a result, the car becomes less comfortable to ride in, and its ride height is lowered. Thus, a large gas leak makes it hard to maintain the original performance of the suspension system. To cope with this, gas must be resupplied or resealed into the gas chamber inside the cylinder housing. Resupply of gas, however, entails much trouble.